More than one-fourth of workers surveyed by Harris Interactive said they plan to shop online from work on Black Friday or Cyber Monday.

Overall, according to the survey commissioned earlier this fall by CareerBuilder, not quite half of workers expect to spend work time this month doing some Internet shopping.

Actually, the survey found that Cyber Monday is likely to be just the startup of an online buying flurry. Nearly a third of the survey respondents said they were most likely to shop from work after Dec. 7.

Human resource officials said it’s a good time for employers to remind employees of any relevant Internet use policies. About one-fourth of workplaces have fired workers for violating online rules.

The survey found that 7 percent of hiring managers have fired an employee specifically for doing holiday shopping at work, so it behooves workers to know what’s acceptable.

Online shopping isn’t the only possible concern. Social media use is the biggest source of disciplinary trouble for workers. Again, it pays to know the rules.

Many workplaces have fairly relaxed Internet use policies, understanding that workers have a personal life as well as a work life. That doesn’t mean there’s blanket acceptance for doing personal business on the employer’s time.

In fact, the CareerBuilder report said, about one-third of employers keep tabs on employee activity by monitoring email use at work.